Maurice, if the slide is not milled for optics, you can replace the rear sight with a Dovetail based Optics Plate : I would contact TruGlo for information on 1911/2011 Pistols : truglo.com/blog/post/truglo-inc.-offers-pistol-dovetail-optic-mount

For features and value id go with a Holosun 507C with accs vulcan reticle, for bomb proof durability a holosun 508T or Trijicon RMR, are all great options, all 3 of those optics all have the RMR footprint,
If your pistol is not milled to accept a reddot Parker mountain can mill it for any optic you choose.
parkermountainmachine.com/store/c75/PMM_Pistol_Slide_Service.html
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Rmr available here
budsgunshop.com/product_info.php/products_id/40001/trijicon+700672+rmr+1x+unlimited+eye+relief+325+moa+black />-----------
Holosun 507C here
primaryarms.com/holosun-hs507c-v2-acss-pistol-red-dot-sight-acss-reticle
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508T
Here
kenziesoptics.com/product/holosun-micro-green-dot-he508t-gr/